Oil and gas pipelines are extremely important for delivery of oil and gas from the source to the consumer. Such pipelines must accommodate large quantities of oil and gas, be able to withstand various pressures, and are at times, subject to surges of pressure. Pressure surges also known as pressure surge waves or “water hammers,” are caused by various factors, such as, rapid opening or closure of a valve or starting or stopping of a pump. Thus, pipelines are equipped with surge relief valves to accommodate and handle pressure surges.
Surge relief valves must respond very quickly and smoothly to pressure surges. The surge relief valves must open quickly to track the large initial pressure rise and then close in direct response to pressure decrease at the valve inlet, relieving sufficient fluid volume to eliminate the surge. The excess fluid is typically diverted to a storage vessel and then returned to the product line.
It has been known to provide a dynamically balanced-plug assembly that slides back and forth easily and rapidly to open, close and throttle. Pressure in the plug cavity closes the valve while lack of pressure opens the valve. Typically, the cavity behind the valve plug is filled with nitrogen gas to affect proper relief set pressure of the valve and hold the valve's internal plug or piston, tight against its seat. This cavity loading force seats the valve and opposes the force generated by line pressure in front of the valve. The valve remains closed until the surge wave pressure exceeds the force behind the plug (set pressure). The surge relief valve then opens to track the surge.
Thus, the seals in the valves must be seated properly and provide a tight seal, preventing fluid flow leaks under both steady state conditions and surges. In order to properly function, it is advantageous for the mating surfaces within the valve to engage with a relatively high degree of precision without slippage or gaps.
Oftentimes, it is difficult to provide a seal that functions across a range of pressures and temperatures, is compatible with a variety of fluids, allows the valve to be opened and closed with minimal effort, and is sufficiently wear resistant to withstand repeated opening and closing operations. Accordingly, it is desirable to provide a seal for surge relief valves, and all valves in general, that can withstand high pressure applications, operate over long periods of time, and forms a tight seal that reduces or eliminates fluid leak around the seal.